(1) Field of the Invention
This invention relates to a process for preparing a printed-circuit board, and more particularly, to an improved process for preparing a printed-circuit board, in which water, solvent, neutralizing agent, etc. contained in a photosensitive resist film are reduced to improve stickiness of the photosensitive resist film.
(2) Description of the Prior Art
A process for preparing a printed-circuit board, in which an electrodeposited photosensitive resist is subjected to an electrodeposition coating, is known (see U.S. Pat. No. 3954587, U.S. Pat. No. 4592816, U.S. Pat. No. 4632900, U.S. Pat. No. 4673458, Japanese Patent Application Laid-Open Nos. 207139/85, 206293/86, 6070/88, etc.).
However, in the case where the above photosensitive resist is used, since a resist film is formed according to one-stage electrodeposition coating, when a pattern mask film in the form of a negative film or a positive film is lapped on the coated resist film to be exposed to light, both films easily stick together. Particularly, the both films are influenced by a temperature at which they are handled, and, in the worst case, both films stick together to such an extent that it is difficult for the pattern mask to be released and marks are formed on the resist film, often resulting in making automation difficult and in increasing occurrences of failures in circuit.
In order to prevent the above troubles, it may be considered to increase a glass transition temperature of a resin used in the electrodeposited resist. However increase in the glass transition temperature results in raising such problems that a film resistance at the time of electrodeposition coating is so increased as to make it impossible to obtain a satisfactory film thickness and that even if ultraviolet light is irradiated when exposed to light, curing properties of the film become poor and photosensitive properties are reduced.
On the other hand, in the case of an electrodeposition-coated positive photoresist, even a film in its unexposed area, too, has a polar group such as carboxyl group, amino group or the like and has a water-soluble property, resulting in raising such a problem that difference in solubilities in a developing solution between an exposed area and an unexposed area is smaller compared with a solvent based positive resist. Therefore, in order to obtain a satisfactory printed-circuit board by use of the electrodeposition-coated positive photoresist, it is necessary to strictly control surface characteristics of the photoresist, for example, by controlling solubility of the film in the developing solution or by making the film thickness uniform.
Generally, the electrodeposition-coated resist film contains water, solvent, neutralizing agent, etc. When they remain in the resist film, it has poor slickness and easily sticks to the pattern mask film. Therefore, it is a common practice to employ a drying step to evaporate the above volatile matters after the step of electrodeposition coating. However, if the drying is carried out at high temperatures or for a long time, the resist may react, often result in failures in development.